Detection of coil coupling in an inductive charging system

ABSTRACT

An inductive charging system can include a transmitter device and a receiver device. The transmitter device may be adapted to detect when a receiver coil in the receiver device is coupled to a transmitter coil in the transmitter device. For example, the current input into a DC-to-AC converter in the transmitter device can be measured and coil coupling detected when the current equals or exceeds a threshold value.

TECHNICAL FIELD

The invention relates generally to inductive charging systems, and moreparticular to detecting coil coupling in an inductive charging system.

BACKGROUND

Many electronic devices include one or more rechargeable batteries thatrequire external power to recharge from time to time. Often, thesedevices may be charged using a similar power cord or connector, forexample a universal serial bus (“USB”) connector. However, despitehaving common connection types, devices often require separate powersupplies with different power outputs. These multiple power supplies canbe burdensome to use, store, and transport from place to place. As aresult, the benefits of device portability may be substantially limited.

Furthermore, charging cords may be unsafe to use in certaincircumstances. For example, a driver of a vehicle may become distractedattempting to plug an electronic device into a vehicle charger. Inanother example, a charging cord may present a tripping hazard if leftunattended.

To account for these and other shortcomings of portable electronicdevices, some devices include an inductive charging system. The user maysimply place the device on an inductive charging surface of a chargingdevice in order to charge the battery. The charging device can detectthe presence of the electronic device on the inductive charging surfaceby pinging or transmitting power to the electronic device for a giventime period and waiting to receive a response (e.g., a communicationsignal) from the electronic device. If the electronic device is not onthe inductive charging surface, a response is not received from theelectronic device and the charging device stops pinging. The chargingdevice may then ping periodically until a communication signal isreceived from the electronic device.

Periodic pinging, however, consumes power and can reduce the charge onthe battery. For example, if the electronic device is not present fortwelve hours, periodic pinging can consume power needlessly. The timeinterval between pings can be increased to save power, but this slowsthe response time of the charging device. For example, the chargingdevice can ping every minute, but up to a minute can pass before thecharging device responds by transmitting power to the electronic device.

SUMMARY

In one aspect, a receiver device for use in an inductive charging systemcan include a receiver coil operatively connected to an input of anAC-to-DC converter, a first resonant circuit operatively connected inseries between the receiver coil and the input of the AC-to-DCconverter, and a second resonant circuit operatively connected inparallel with the receiver coil between the receiver coil and the inputto the AC-to-DC converter. A load may be operatively connected to anoutput of the AC-to-DC converter. As one example, the load can be arechargeable battery. The first resonant circuit is associated with afirst resonant frequency and the second resonant circuit is associatedwith a second resonant frequency that is different from the firstresonant frequency. In one embodiment, the second resonant frequency ishigher than the first resonant frequency.

In another aspect, a switch may be operatively connected in series withthe second resonant circuit in the receiver device. A processing devicein the receiver device can control the state of the switch. The switchcan be used to communicate with the transmitter device. As one example,the switch can be opened when the receiver device is to be “cloaked” ornot in communication with the transmitter device, even when the receivercoil is able to couple with the transmitter coil (e.g., the receiverdevice is on the charging surface). As one example, the transmitterdevice can transfer energy to the receiver device to charge a battery inthe receiver device. The switch is closed while the battery is charging.The switch can be opened when the battery is charged fully to inform thetransmitter device to stop transferring energy. The transmitter devicemay then enter a low power or sleep state in response to the open stateof the switch.

In another aspect, a method for detecting coupling between a receivercoil and a transmitter coil in an inductive power transfer system caninclude a transmitter device transmitting pings to a receiver device atdifferent frequencies and measuring a current input into a DC-to-ACconverter in the transmitter device based on each ping. The currentmeasurements can then be analyzed to determine whether a currentmeasurement indicates the receiver coil and the transmitter coil areinductively coupled. As one example, the current input into the DC-to-ACconverter can be higher when the receiver and transmitter coils arecoupled than when the receiver and transmitter coils are not coupled.

In yet another aspect, a receiver in an inductive charging system caninclude a resonant circuit connected in parallel with a receiver coil. Aswitch can be connected in series with the resonant circuit. A methodfor operating a transmitter device can include the transmitter devicetransferring energy to the receiver device when the switch is closed,and the transmitter device responsively taking a different action whenthe switch is open. In one embodiment, the different action can includethe transmitter device entering a low power state when the switch isopen. Additionally or alternatively, the different action may includethe transmitter device periodically transmitting one or more pings tothe receiver device.

In another aspect, an inductive charging system can include atransmitter device and a receiver device. The transmitter device caninclude a current sense operatively connected between an output of apower supply and an input of a DC-to-AC converter. A method foroperating the inductive charging system can include detecting a changein a current that is input into the DC-to-AC converter and transferringenergy based on the current change. The energy transfer can stop when aresponse is not received from a receiver device. One or more operationsin the transmitter device can be adaptively adjusted based on notreceiving a response from the receiver device. For example, the timeinterval between pings can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are better understood with reference to thefollowing drawings. The elements of the drawings are not necessarily toscale relative to each other. Identical reference numerals have beenused, where possible, to designate identical features that are common tothe figures.

FIG. 1 illustrates one example of inductive charging system;

FIG. 2 depicts a simplified block diagram of one example of theinductive charging system 100 shown in FIG. 1;

FIG. 3 depicts a simplified block diagram of another example of theinductive charging system 100 shown in FIG. 1;

FIG. 4 is a flowchart of a method for scanning a frequency range todetect coil coupling;

FIG. 5 is a flowchart of one method for operating an inductive chargingsystem; and

FIG. 6 is a flowchart of another method for operating an inductivecharging system.

DETAILED DESCRIPTION

Embodiments described herein can transfer energy inductively from atransmitter device to a receiver device to charge a battery or tooperate the receiver device. Additionally or alternatively,communication or control signals can be transmitted to the receiverdevice through the inductive coupling between the transmitter andreceiver coils. For example, while charging, high frequency pulses canbe added on top of the inductive charging frequency to enable bothcharging and communication. Alternatively, the transferred energy can beused solely for communication. Thus, the terms “energy”, “signal”, or“signals” are meant to encompass transferring energy for wirelesscharging, transferring energy as communication and/or control signals,or both wireless charging and the transmission of communication and/orcontrol signals.

Referring now to FIG. 1, there is shown a top view of one example of aninductive charging system. The inductive charging system 100 includes acharging device 102 and an electronic device 104. In the illustratedembodiment, the charging device 102 is depicted as a charging dock andthe electronic device as a smart telephone. The electronic device and/orthe charging device can be implemented as different devices in otherembodiments. For example, the electronic device 104 can be a digitalmedia player, a wearable electronic or communication device, a healthmonitoring device, a tablet computing device, and any other type ofelectronic device that includes one or more inductive charging coils. Asanother example, the charging device 102 may be adapted to be insertedinto a charging port in an electronic device.

To transfer energy to the electronic device 104, the electronic device104 is placed on a charging surface 106 of the charging dock 102. Thecharging dock 102 may be connected to a power source (e.g., a walloutlet) through a power cord or connector (not shown). The charging dock102 includes one or more inductive charging coils that transfer signalsor energy to one or more inductive charging coils in the electronicdevice 104. Energy can be transferred, for example, to charge a batteryin the electronic device 104 or to operate the electronic device.Additionally or alternatively, control and/or communication signals canbe transferred wirelessly between the charging dock 102 and theelectronic device 104. Thus, in the illustrated embodiment the chargingdock 102 is a transmitter device with a transmitter coil or coils andthe portable electronic device 104 is a receiver device with one or morereceiver coils.

FIG. 2 depicts a simplified block diagram of one example of theinductive charging system 100 shown in FIG. 1. The charging device 102includes a power supply 200 operably connected to a DC-to-AC converter202. Any suitable type of a DC-to-AC converter may be used in one ormore embodiments. For example, the DC-to-AC converter is constructed asan H bridge in one embodiment.

An input of a current sense circuit 204 is connected to an output of thepower supply 200, and the output of the current sense circuit 204 isconnected to an input of the DC-to-AC converter 202. An input of anamplifier 206 is operably connected to an output of the current sensecircuitry 204, and the output of the amplifier 206 is operably connectedto a processing device 208. The processing device can be implemented asany electronic device capable of processing, receiving, or transmittingdata or instructions. For example, the processing device 208 can be amicroprocessor, a central processing unit (CPU), an application-specificintegrated circuit (ASIC), a digital signal processor (DSP), orcombinations of multiple such devices. As described herein, the term“processing device” is meant to encompass a single processor orprocessing unit, multiple processors, multiple processing units, orother suitably configured computing element or elements.

The processing device 208 may also be operably connected to the DC-to-ACconverter 202. The processing device 208 can control the operation ofthe DC-to-AC converter 202 in some embodiments. The output of theDC-to-AC converter 202 is operably connected to the transmitter coil210.

The electronic device 104 can include a receiver coil 212 operablyconnected to an AC-to-DC converter 214. Any suitable type of AC-to-DCconverter may be used in one or more embodiments. For example, theAC-to-DC converter is constructed as a diode bridge in one embodiment. Aload 216 is operably connected to the output of the AC-to-DC converter214. The load 216 is a rechargeable battery in one embodiment. Adifferent type of load can be used in other embodiments.

The transmitter coil 210 and the receiver coil 212 together form atransformer 218. The transformer 218 transfers energy through inductivecoupling between the transmitter coil 210 and the receiver coil 212.Essentially, energy is transferred from the transmitter coil 210 to thereceiver coil 212 through the creation of a varying magnetic flux by theAC signal in the transmitter coil 210 that induces a current in thereceiver coil 212. The AC signal induced in the receiver coil 212 isreceived by the AC-to-DC converter 214 that converts the AC signal intoa DC signal. In embodiments where the load 122 is a rechargeablebattery, the DC signal is used to charge the battery.

In some embodiments, the leakage inductance of the transformer 218 canbe significant. Resonant circuits may be included in the inductivecharging system 100 to cancel some or all of the leakage inductance whenthe capacitance and inductance values are near the resonant frequency(f_(R1)). In the illustrated embodiment, the resonant circuit in thetransmitter device 102 is a resonant capacitor C_(RP) connected inseries between the DC-to-AC converter 202 and the transmitter coil 210.The resonant circuit in the receiver device 104 is a resonant capacitorC_(RS1) connected in series between the receiver coil 212 and theAC-to-DC converter 214.

In some embodiments, the transmitter device 102 may scan the environmentto detect the presence of the receiver device 104 when the transmitterdevice is not inductively coupled to the receiver device (e.g., nottransferring energy to the receiver device). To scan the environment,the transmitter device 102 can transfer a short burst of energy to thereceiver device 104 to determine if the receiver coil 212 is coupled tothe transmitter coil 210. This short burst of energy is known as a ping.The transmitter device 102 may transmit a ping and wait for a responsefrom the receiver device 104. If no response is received, thetransmitter device 102 waits for a given period of time before sendinganother ping. If a response is received, the transmitter device 102 cantransfer energy to the receiver device 104 to charge a battery and/or totransmit one or more communication signals to the receiver device 104.

In some embodiments, a second resonant circuit is included in thereceiver device 104 to reduce the amount of power consumed by thetransmitter coil 210 when transmitting pings. In the illustratedembodiment, the second resonant circuit is a second resonant capacitorC_(RS2) connected in parallel with the receiver coil 212 between thereceiver coil and the AC-to-DC converter 214. The second resonantcircuit can have a resonant frequency (f_(R2)) that is higher than theresonant frequency (f_(R1)) of the first resonant circuits C_(RP) andC_(RS1). In other words, f_(R1)<f_(R2). As one example, the lower firstresonant frequency approximately 250 kHz and the second higher resonantfrequency (f_(R2)) can be in the range of 750 kHz to 1 MHz. Otherembodiments can operate at different frequencies and/or frequencyranges.

Other embodiments can configure the resonant circuits differently. Theresonant circuits can include additional or different components. Theresonant circuits can be included at different locations or connected ina different circuit configuration within the transmitter and/or receiverdevice.

The transmitter coil 210 can be energized at the higher second resonantfrequency (f_(R2)) when transmitting a ping and draw relatively lowcurrent when the inductance of the transmitter coil is low. At thehigher second resonant frequency the impedance of the transmitter coil210 is higher and the transmitter coil does not consume as much powerwhen transmitting pings.

When the pings are transmitted at the second resonant frequency, thetransmitter device 102 can determine whether the receiver coil 212 iscoupled to the transmitter coil 210 by measuring the current input intothe DC-to-AC converter 202. When the receiver coil 212 is coupled to thetransmitter coil 210, a higher current can be input into the DC-to-ACconverter than when the receiver coil 212 is not coupled to thetransmitter coil 210. The processing device 208 can receive currentmeasurements from the current sense circuit 204 and based on an analysisor review of the current measurements, determine whether the receivercoil 212 is coupled to the transmitter coil 210.

Referring now to FIG. 3, there is shown a simplified block diagram ofanother example of the inductive charging system 100 shown in FIG. 1.The inductive charging system is similar to the embodiment shown in FIG.2 except for the switch 300 connected in series with the second resonantcapacitor C_(RS2). Any suitable type of switch can be used. In someembodiments, a processing device 302 can control the state of the switch300 (i.e., open or closed). Like the processing device 208 in FIG. 2,the processing device 302 can be implemented as any electronic devicecapable of processing, receiving, or transmitting data or instructions.

The switch 300 can be used by the receiver device to communicate withthe transmitter device. As one example, the switch can be opened whenthe receiver device 104 is to be “cloaked” or not in communication withthe transmitter device 102, even when the receiver coil is able tocouple with the transmitter coil (e.g., the receiver device is on thecharging surface). As one example, the transmitter device 102 cantransfer energy to the receiver device 104 to charge a battery (e.g.,load 216) in the receiver device. The switch 300 is closed while thebattery is charging. The switch can be opened when the battery ischarged fully to inform the transmitter device 102 to stop transferringenergy. The transmitter device 102 may enter a low power or sleep statein response to the open state of the switch 300. The transmitter device102 can wake up periodically to transmit a ping to the receiver device104. If the switch 300 is closed, the processing device 208 in thetransmitter device 102 can detect the receiver device based on one ormore current measurements received from the current sense circuit 204.

In some embodiments, the resonant frequency can vary due variousreasons, such as manufacturing tolerances and coupling differencesbetween different receiver and transmitter coils. As one example, theresonant frequency can vary up to 50 kHz. Thus, in some embodiments, thetransmitter device can sweep or scan a given range of frequencies todetermine a frequency at which a maximum current is input into theDC-to-AC converter. For example, a higher resonant frequency can be setto 1 MHz, and the transmitter device may scan a frequency range of 800kHz to 1.2 MHz.

FIG. 4 is a flowchart of a method for scanning a frequency range todetect coil coupling. Initially, the transmitter device transmits one ormore pings to a receiver device at a given frequency and the currentinput into the DC-to-AC converter in the transmitter device is measured(blocks 400 and 402). A determination may then be made at block 404 asto whether or not the frequency scan is complete. If not, the processcan pass to block 406 where the frequency is adjusted. The methodreturns to block 400 and repeats until the frequency scan is complete.

When the frequency scan is complete, the current measurements canoptionally be processed at block 408. As one example, if multiplecurrent measurements are taken at each frequency, the currentmeasurements measured at a particular frequency can be averagedtogether. The current measurements are then analyzed at block 410. Adetermination can be made at block 412 as to whether or not a currentmeasurement equals or exceeds a threshold value. The threshold value canbe a minimum or expected current measurement that indicates the receivercoil is coupled to the transmitter coil. The method may end if a currentmeasurement does not equal or exceed the threshold value. Couplingbetween a transmitter and receiver coil is indicated when a currentmeasurement equals or exceeds the threshold value (block 414) and themethod ends.

Referring now to FIG. 5, there is shown a flowchart of one method foroperating an inductive charging system. Initially, the transmitterdevice can transmit one or more pings to the receiver device (block500). The current measurements can optionally be processed at block 502.As one example, if multiple current measurements are taken at aparticular frequency, the current measurements can be averaged together.

A determination may then be made at block 504 as to whether or not theswitch (i.e., switch 300 in FIG. 3) in the receiver device is open orclosed. If the switch is open, the process can pass to block 506 wherethe transmitter device waits for a given period of time. The method maythen return to block 500 and repeat until the transmitter detects theswitch is closed.

When the switch is closed, the process continues at block 508 where thetransmitter device can transmit energy to the receiver device. Thetransferred energy can be used to charge a battery in the receiverdevice, to operate the receiver device, and/or to transmit control orcommunication signals to the receiver device. A determination may thenbe made at block 510 as to whether or not the switch remains closed orhas been opened. If the switch remains closed, the method can check thestate of the switch continuously, periodically, or at select times. Whenthe switch is opened, the process may pass to block 512 where thetransmitter device can take one or more actions based on the open stateof the switch. For example, in one embodiment, the transmitter devicemay enter a low power state, such as a sleep state or an off state.

FIG. 6 is a flowchart of another method for operating an inductivecharging system. In one embodiment, this method can be used todistinguish between a foreign object and a receiver device positioned ona charging surface of the transmitter device. Initially, the transmitterdevice may detect an increase in the current that is input into theDC-to-AC converter at block 600. The increased current can initially beinterpreted as a receiver coil coupling with the transmitter coil in thereceiver device. Based on the increased current and the preliminaryinterpretation, the transmitter device can begin transferring energy atblock 602. A determination is then made at block 604 as to whether ornot a response is received from a receiver device. The method ends if aresponse is received from a receiver device.

When a response is not received, the transmitter device can change theinitial interpretation and assume a receiver coil is not coupled to thetransmitter coil and responsively stop the transfer of energy (block606). The transmitter device may then adjust one or more operationsbased on the lack of a response. For example, in one embodiment, thetransmitter device may increase the time interval between pings to savepower. Additionally or alternatively, the threshold value for indicatingcoil coupling (see block 412 in FIG. 4) can be adjusted (e.g.,increased). Different actions may be taken in other embodiments.

The flowcharts in FIGS. 4-6 can be performed differently in otherembodiments. Blocks can be added, omitted, or re-order in someembodiments. In one example, block 408 in FIG. 4 can be omitted or block408 can be performed before block 404. Block 502 in FIG. 5 can beomitted as another example.

Embodiments disclosed herein have been described with respect to thesecond resonant frequency being higher than the first resonantfrequency, and the current input into the DC-to-AC converter in thetransmitter device being a higher or increased current when indicatingcoil coupling. Other embodiments, however, are not limited to thisimplementation. In some embodiments, the second resonant frequency canbe lower than the first resonant frequency (f_(R1)>f_(R2)), and whenindicating coil coupling, the current input into the DC-to-AC convertercan be a smaller or reduced current. In such embodiments, the currentvalue that indicates coil coupling can be lower than a threshold value.

Various embodiments have been described in detail with particularreference to certain features thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the disclosure. And even though specific embodiments have beendescribed herein, it should be noted that the application is not limitedto these embodiments. In particular, any features described with respectto one embodiment may also be used in other embodiments, wherecompatible. Likewise, the features of the different embodiments may beexchanged, where compatible.

We claim:
 1. A receiver device for use in an inductive charging system,comprising: a receiver coil operatively connected to an input of anAC-to-DC converter; a rechargeable battery operatively connected to anoutput of the AC-to-DC converter; a first resonant circuit operativelyconnected in series between the receiver coil and the input of theAC-to-DC converter, the first resonant circuit associated with a firstresonant frequency; a second resonant circuit operatively connected inseries across leads of the first resonant circuit, the second resonantcircuit associated with a second resonant frequency that is differentfrom the first resonant frequency; and a switch configured to: connectthe second resonant circuit across the leads of the first resonantcircuit when the receiver device is receiving power; and disconnect thesecond resonant circuit from the first resonant circuit when therechargeable battery is fully charged.
 2. The receiver device as inclaim, further comprising a processing device for controlling a state ofthe switch.
 3. The receiver device as in claim 1, further comprising aload operatively connected to an output of the AC-to-DC converter. 4.The receiver device as in claim 3, wherein the load comprises therechargeable battery.
 5. The receiver device as in claim 1, wherein thefirst and second resonant circuits each comprise a capacitor.
 6. Thereceiver device as in claim 1, wherein the AC-to-DC converter comprisesa four diode bridge circuit.
 7. The receiver device as in claim 1,wherein the second resonant frequency is higher than the first resonantfrequency.
 8. A receiver device for use in an inductive charging system,comprising: a receiver coil operative to receive inductive power; afirst resonant circuit operatively connected in series with the receivercoil and associated with a first resonant frequency; and a secondresonant circuit coupling an output of the first resonant circuit to alead of the receiver coil, the second resonant circuit associated with asecond resonant frequency that is higher than the first resonantfrequency; wherein: the second resonant circuit is associated with alow-power mode of a transmitter device coupled to the receiver device.9. The receiver device of claim 8, further comprising an electronicswitch connected in series with the second resonant circuit.
 10. Thereceiver device of claim 9, wherein the electronic switch is configuredto connect or disconnect the second resonant circuit from the receivercoil.
 11. The receiver device of claim 9, wherein the first resonantcircuit is configured to resonate with a third resonant circuitassociated with the transmitter device.
 12. The receiver device of claim11, wherein the transmitter device comprises a coil coupled in serieswith the third resonant circuit.
 13. The receiver device of claim 12,wherein the electronic switch disables the second resonant circuit tocloak the receiver device from the transmitter device.
 14. A receiverdevice for use in a wireless charging system, the receiver devicecomprising: a processor; a rechargeable battery in communication withthe processor; an inductive coil in communication with the processor andthe rechargeable battery; a first capacitor connected in series with afirst lead of inductive coil; a second capacitor coupling an output leadof the first capacitor to a second lead of the inductive coil; and aswitch connected in series with the second capacitor and incommunication with the processor; wherein the processor is configured tosend a signal to the switch to disconnect the second capacitor from thereceiver coil when the rechargeable battery is charged beyond athreshold.
 15. The receiver device of claim 14, further comprising ahousing at least partially enclosing the processor and the inductivecoil.
 16. The receiver device of claim 14, wherein the first capacitoris configured to resonate at a first frequency with a third resonantcircuit associated with a transmitter device.
 17. The receiver device ofclaim 16, wherein the second capacitor is configured to resonant at asecond frequency different from the first frequency.
 18. The receiverdevice of claim 17, wherein the second frequency is greater than thefirst frequency.